The present invention relates generally to devices and methods useful in treating patients with stroke or occlusive cerebrovascular disease. More specifically, the invention provides an extracranial device capable of reversing flow down an internal carotid artery, and into the external carotid artery during an invasive carotid procedure, thereby avoiding distal embolization of vascular debris. Various diagnostic or therapeutic instruments, including an atherectomy catheter, a filter, and/or an angioplasty/stent catheter, can be introduced through the device for treating the carotid occlusion. The invention may also be useful to reverse flow during a stroke.
Stroke is the third most common cause of death in the United States and the most disabling neurologic disorder. Approximately 700,000 patients suffer from stroke annually. Stroke is a syndrome characterized by the acute onset of a neurological deficit that persists for at least 24 hours, reflecting focal involvement of the central nervous system, and is the result of a disturbance of the cerebral circulation. When a patient presents with neurological symptoms and signs which resolve completely within 1 hour, the term transient ischemic attack (TIA) is used. Etiologically, TIA and stroke share the same pathophysiologic mechanisms and thus represent a continuum based on persistence of symptoms and extent of ischemic insult.
Outcome following stroke is influenced by a number of factors, the most important being the nature and severity of the resulting neurologic deficit. Overall, less than 80% of patients with stroke survive for at least 1 month, and approximately 35% have been cited for the 10-year survival rates. Of patients who survive the acute period, up to 75% regain independent function, while approximately 15% require institutional care.
Hemorrhagic stroke accounts for 20% of the annual stroke population. Hemorrhagic stroke often occurs due to rupture of an aneurysm or arteriovenous malformation bleeding into the brain tissue, resulting in cerebral infarction. The remaining 80% of the stroke population are hemispheric ischemic strokes and are caused by occluded vessels that deprive the brain of oxygen-carrying blood. Ischemic strokes are often caused by emboli or pieces of thrombotic tissue that have dislodged from other body sites or from the cerebral vessels themselves to occlude in the narrow cerebral arteries more distally. The internal carotid artery, commonly affected by atherosclerosis causing symptomatic occlusion in the arterial lumen, is often responsible for hemispheric ischemic stroke and generating thromboembolic material downstream to the distal cerebral vessels. Treatment of the occluded carotid artery in patients with stroke and TIA or for stroke prevention in patients with asymptomatic flow limiting carotid stenosis undergoing major cardiothoracic surgeries includes performing angioplasty, stent placement, or atherectomy on the occluded carotid artery. Unfortunately, placing instrumentation within a diseased carotid artery is associated with increased risk of ischemic stroke, since manipulation of an atheromatous plaque in the arterial wall often causes emboli to dislodge distally in the narrow cerebral arteries.
Current methods of preventing distal embolization from carotid instrumentation include insertion of a blood filter distal to the occlusion and suctioning embolic debris during the procedures. Disadvantages associated with the conventional methods are that (1) inserting the filter through the atheromatous lesion is associated with increased risk of distal embolization, (2) using suction to reverse the flow in the internal carotid artery may increase a patient""s blood loss if the suctioned blood is discarded, and (3) systemic anticoagulation and pumping may be required to recycle the suctioned blood back into the arterial or venous system, and such anticoagulation is associated with increased risk of hemorrhage.
New devices and methods are thus needed in patients undergoing carotid procedures for definitive or prophylactic treatment of carotid plaque, which minimize the risk of distal embolization and prevent ischemic stroke.
The invention provides devices and methods for preventing ischemic stroke in patients undergoing invasive carotid procedures, including angioplasty, stent placement, and/or filter insertion, by reversing blood flow down an internal carotid artery and up the ipsilateral external carotid artery. In this way, embolic debris generated as a result of placing instrumentation within a diseased carotid artery is diverted to the external carotid artery, thereby preventing stroke by minimizing distal embolization to the narrow cerebral vessels. The devices and methods are also useful to remove an embolus and improve flow (by reversing collateral blood flow across the circle of Willis) in patients with acute stroke.
One embodiment of the medical device comprises a catheter and two expandable occlusion members. The catheter has a lumen communicating with a proximal end and a distal port at its distal end. The lumen is adapted for insertion of a therapeutic instrument, such as an angioplasty, stent, and/or blood filter catheter. An occluder is mounted near the distal end of the catheter proximal to the port. A constrictor is mounted near the distal end of the catheter distal to the port. The expandable occluder and constrictor may be elastomeric balloons. Each of the balloon occluder and constrictor communicates with an inflation lumen and an inflation port at the proximal end of the catheter. The constrictor may be a toroidal balloon or a device of any other appropriate shape, so that it allows passage of blood. The constrictor is mounted on a second member which is slidably insertable through the catheter, and passes beyond the occluder. In this way, the second member and the constrictor are moveable longitudinally relative to the first occluder. In other embodiments, the constrictor may consist of a balloon having more than one opening at its center for the passage of blood, or may consist of more than one expandable balloons allowing passage of blood through the gap between the arterial wall and the expanded balloons.
In another embodiment, a manometer is mounted distal to the occluder for monitoring blood pressure between the occluder and the constrictor. A second manometer may be mounted distal to the constrictor for monitoring blood pressure distal to the constrictor. The proximal end of the catheter may include a hemostatic valve.
In still another embodiment, the catheter includes a second lumen communicating with a proximal end and an infusion port at its distal end. The port is located distal to the distal port of the catheter. The second lumen and its port are adapted for delivering a pharmaceutical agent to the carotid artery, including an angiographic dye.
In still another embodiment, a second or distal occluder includes a shunt for the passage of blood therethrough. The shunt comprises a tube having a lumen communicating with a proximal end and a distal end. A pump is operably associated with the shunt to facilitate delivery of blood from the proximal end of the shunt to the distal end of the shunt, thereby moving blood through the second occluder. The pump may be a helical screw pump included in the lumen of the shunt. The pump may be heparin coated to prevent thrombi formation.
The invention provides methods for reversing flow in a carotid artery which branches into first and second distal segments, where the first distal segment has an atheromatous lesion. More specifically, the methods are useful in reversing flow down an internal carotid artery (ICA) and up the external carotid artery (ECA), where both the ICA and the ECA are distal segments of the common carotid artery (CCA). In a first method, using the devices described above, the distal end of the catheter is inserted into the CCA. The catheter can be inserted over a guide wire through an incision on a peripheral artery, including the femoral artery, the subclavian artery, the brachiocephalic artery, or the common carotid artery. The catheter is positioned to locate the occluder within the CCA, and then to locate the constrictor within the ECA by operating the second member and the constrictor through the catheter. Preferably, the occluder is expanded to completely or partially occlude the CCA. At a critically low CCA pressure, blood flow in the ICA is reversed to pass over the atheromatous lesion and into the ECA. The flow reversal can be verified fluoroscopically with dye. If flow reversal fails to occur or if augmentation of flow reversal is desired, the ECA constrictor is expanded, further reducing the pressure in the ECA to facilitate reversal of flow down the ICA and into the ECA. In an alternative yet less preferred embodiment, the constrictor is expanded to occlude the ECA. The occluder is then partially or completely expanded, causing a decline in the CCA pressure. At a critically low CCA pressure, blood flow in the ICA is reversed to pass over the atheromatous lesion and into the ECA.
After blood reversal is confirmed, procedures on either the ICA or bifurcation of the CCA can be performed by advancing a therapeutic or diagnostic instrument through the lumen and port of the catheter distal to the occluder. An atherectomy catheter, for example, can be introduced to remove the atheroma in the ICA without fear of distal embolization.
In another method, using the device having a second occluder including a shunt for the passage of blood therethrough, the catheter is inserted in the carotid artery, with the second occluder located in the ECA and the first occluder located in the CCA. Preferably, the first occluder is expanded to occlude the CCA followed by expansion of the second occluder to occlude the ECA. Alternatively, the second occluder is expanded to occlude the ECA followed by expansion of the first occluder to occlude the CCA. A pump, traversing the ECA occluder, is activated to facilitate blood reversal from the ICA toward the ECA by moving blood through a shunt included in the second occluder. The flow rate across the second occluder in the ECA can be variably controlled by the pump.
It will be understood that there are several advantages in using the devices and methods disclosed herein for prevention of distal embolization during use of instrumentation in the carotid artery. For example, the devices (1) abolish the need for suction distal to the CCA occluder, thereby minimizing blood loss, (2) eliminate the need for systemic anticoagulation, pumping, and a second arterial or venous stick, all of which are required where suction is employed, (3) can be used to introduce a variety of diagnostic or therapeutic instrument to the carotid artery, (4) can be used in any procedures which require instrumentation within the carotid artery, (5) can be used for definitive treatment of acute or subacute ischemic stroke, (6) can be used in the angiogram or fluoroscopy suite available in most hospitals, and (7) require only one incision site for entry.